Containers for liquefied gases

ABSTRACT

1,110,366. Ships; ship&#39;s fittings &amp;c. CONCH INTERNATIONAL METHANE Ltd. 17 Jan., 1967 [21 March, 1966], No. 12293/66. Headings B7A and B7S. [Also in Division F4] A prismatic non-self-supporting fluid-tight metal tank 7, Fig. 1, for storing liquefied gas, e.g. methane, has an integral external key member 25, Fig. 3, extending along the full length of the junction of each two adjacent side, top, end and bottom walls and referred to as a corner and each key 25 is secured within a keyway 38, Fig. 4, formed in surrounding load-bearing insulation material 5. The tank 7 is made from pre-assembled annular units, each providing a portion of the top, bottom, and side walls 7a, 7b, 7c and are welded together to form expansion joints 24. The surrounding insulation 5 of balsa wood panels 9, plywood 13 and fibreglass is secured to the inner face of the inner hull, the deck 3 and bulkheads 4 of a ship by studs 15. Each key member 25 comprises a tube of quadrant cross-section filled with epoxy resin 28 and each keyway 38 is defined by stop blocks 34, 35 secured to panels 9 and wedges 36, 37.

Jan. 20, 1970 M. M. GIBSON CONTAINERS FOR LIQUEFIED GASES 3 sheets-sheet 1 Filed March 8, 1967 INVENTOR Michael M. Gibson ATTORNEY Jan. 20, 1970 M. M. GIBSON vCONTAINERS FOR LIQUEFIED GASES s sheets-sheet 2 Filed March 8, 1967 INVENTOR Michael M. Gibson BY MM ATTORNEY Jan. 20, 1970 M. M. GIBSON ,3,490,639

v CONTAINERS FOR LIQUEFIED GASES Filed March s, 1967 s sheets-sheet s 27 36 34 |129 I4 2| 7 I2 7G United States Patent O 3,490,639 CONTAINERS FOR LIQUEFIED GASES Michael Merriman Gibson, Tollesbury, England, assigner to Conch International Methane Limited, Nassau, Bahan las, a Bahamian company Filed Mar. 8, 1967, Ser. No. 621,663 Claims priority, application Great Britain, Mar. 21, 1966, 12,293/ 66 Int. Cl. B65d 25/18 U.S. Cl. 220-9 8 Claims ABSTRACT OF THE DISCLOSURE A prismatic tank construction, e.g., for marine use in transporting liqueed gas at cryogenic temperatures, cornpn'sing tank walls of solid load bearing insulation such as balsa wood, supporting a primary membrane of thin metal sheet attached at the corners to elongated anchoring keys which are supported in respective slots formed by adjacent wall edges at a corner between two adjacent walls.

This invention relates to containers for the transport of cold liquids, for example liquetied gases, such as liquefied natural gas, and of the kind comprising a prismatic housing of solid load bearing thermal insulation and a primary and/ or secondary barrier in the form of a thin prismatic Huid-tight membrane or tank of sheet metal which is not self-supporting but is supported by the surrounding solid insulation. Such containers are used, for example, in marine tankers, for the transport of liqueiied gases.

The walls of the membrane or tank of such a container tend to contract substantially when contacted by the cold liquid, i.e., are subject to thermal stresses. However, the invention is exclusively concerned with such containers of the kind in which the membrane tank is held against dimensional change so that the overall dimensions of the membrane remain unchanged and the membrane remains in contact with and supported by the insulation. In this case, the load upon the means anchoring the membrane against overall dimensional change is considerable. The load due to thermal stress is reduced, but is still considerable, if the membrane consists mainly or entirely of metal having a low coeiiicient of thermal expension, e.g., the 36% nickel iron alloy known as Invar, and/or if the Walls of the membrane are provided with expansion joints or formations which provide a large excess of metal accommodating contraction and relieving the thermal stress. Moreover, where the container is mounted in the hold of a marine tanker at least some of the walls of the membrane are subject to stresses caused by ship strains when the tanker is at sea which also contribute to the load upon the means anchoring the membrane against dimensional change. Stresses due to ship strains may be partially reduced by the provision of expansion joints or formations in the membrane. Thus the loads due to thermal and/ or ship stresses upon the means anchoring the membrane against dimensional change are considerable and such anchoring means must be designed to withstand such loads. But, where the container is mounted in the hold of a marine tanker the means anchoring the membrane against overall dimensional change cannot be directly connected to the hull of the tanker because this Would interrupt the insulation and provide heat/cold bridges which would reduce the temperature of the hull with dangerous consequences.

Anchoring means have previously been spaced at intervals along and across the walls of the membrane, but these have not proved very eiiicient. Moreover, there are unbalanced-forces at the corners of the membrane. Thus each corner of the membrane, i.e. the junction formed by 3,490,639 Patented Jan. 20, 1970 ice the edge portions of two adjoining walls, is subject to the loads described above acting in the planes of the two walls and at an angle to and opposing one another at the corner such that the corner is liable to distortion and even collapse.

The object of the present invention is to provide simple but effective means for anchoring the membrane or tank of a container of the kind concerned so as to restrain the corners of the membrane and eiectively hold the membrane against overall dimensional change without prejudicing the heat insulation of the container.

The specic aim of the invention is to provide a marine tanker equipped with one or more containers, the membrane or tank walls of which are at all times supported by the surrounding solid insulation and in which the corners of the membrane are less liable to distortion and collapse.

According to the present invention there is provided a container of the kind concerned, the corners of the membrane of which are anchored to the supporting load-bearing thermal insulation by means of external keys or anchoring members extruding along the corners of the membrane and retained by parts mounted and defining a keyway on the supporting insulation whereby the comers of the membrane are rigidly anchored to the insulation.

It is to be clearly understood that the term corner is used throughout this specication to mean the full length of the junction formed by the edge portions of two adjoining walls.

The external keys or anchoring members may be of any appropriate form. At least some of the Walls of the membrane may each be extended beyond the junction formed with an adjacent Wall and bent over to form a proiiled portion which constitutes a key or anchoring member. Preferably, however, the keys are initially separate components. In one preferred construction each of the keys or anchoring members is constituted by a piece of thin sheet metal which is attached to the external face of a wall adjacent to the junction formed with an adjacent Wall constituting a corner of the membrane, which sheet metal is folded to form a pre-folded proiiled portion which, when filled with load-bearing material, constitutes an anchoring member. Advantageously, the metal is folded to provide an anchoring member of tubular form of any appropriate cross section. In order to it smoothly in the internal corner of the surrounding insulation, the key may conveniently be of quadrant cross section.

As will be described hereinafter, the walls of the membrane may not undergo equal stresses; some undergoing greater stresses than others. Only those walls which are subject to greater stresses need to be provided with anchoring members. However, at least one of two adjacent Walls forming a corner of the membrane will be provided with an anchoring member extending along the said corner. In some cases both adjoining walls forming a corner will require keys at said corner and in this case the adjacent keys may be accommodated in a common keyway in the surrounding insulation. For example, the two adjacent members may each be of small angle segmental cross section so that the two members together form a member of quadrant cross section. In all cases the initially hollow members will be lilled with load bearing material.

The keyway formed in the insulation may be of any appropriate form. For example, the keyway may lbe defined by two blocks or stops secured to two adjacent internal faces of the thermal insulation flanking the internal corner of the insulation and two packing pieces or wedges may be inserted between the two blocks to iiank the anchoring member and form a keyway receiving and retaining the anchoring member in position. It is to be noted that an important feature of the invention is the fact that the corners of the membrane are effectively anchored,

at locations spaced from the corners by the said blocks or stops.

The membrane may be of any appropriate form and material. Throughout this specification the term metal is intended to include alloys. The membrane may be of metal which does not have an unduly low coefficient of thermal expansion but which is for-med with expansion formations, such as corrugations or dimples, in at least one direction providing excess of metal to accommodate contraction. That is to say the excess is taken out when the tank contracts from ambient temperature to the low temperature of liquid housed within the tank. Alternatively, the membrane may be of a metal, such for example as Invar, having a low coefficient of thermal expansion and in which the ratio of elastic stress to thermal stress over the temperature range to which the tank is subjected, and particularly at low temperatures, is equal to or greater than one. Such a membrane may be such that it is not necessary to provide excess metal in the form of expansion joints or formations to accommodate the contraction. In most cases, however, a membrane of such metal will require at least some excess metal in at least one direction.

However, a system of expansion yjoints or formations which accommodates all stresses greatly complicates the structure and increases the cost of the tank. Therefore, in accordance with an important subsidiary aspect of the present invention, the membrane is provided with expansion joints or formations in some of the walls or portions of the walls only, the remaining walls or portions not being provided with such joints or formations. Moreover, the expansion joints or formations which are provided extend in one direction only. That is to say in accordance with this aspect of the invention the walls of the membrance which are subject to greater stresses, i.e. both thermal and ship stresses, when the tanker is at sea, are provided with expansion joints or formations extending in only one direction to accommodate those stresses, whereas the remaining walls which are subject to lesser stresses, that is to say only ther-mal stresses, are not provided with expansion joints or formations thereby simplifying the construction.

In one specific example of a prismatic container having a membrane or tank of Invar and mounted in the cargo hold of a marine tanker the walls of the membrane extending in the longitudinal direction i.e. the fore/ aft axis of the tanker, are provided with expansion joints or formations extending transversely of the said axis, the joints or formations in one wall communicating with the joints or formations in an adjacent wall extending parallel to the said axis. However, the walls extending transversely of the longitudinal axis, i.e., the end walls, are not provided with expansion joints or formations. Such a membrane may be constructed from a plurality of constructional units, each of which is of annular or frame form and has secured thereto narrow strips of the same alloy constituting flanges. The adjacent constructional units are connected together by welding of the free edges of adjacent flanges which constitute the expansion joints. Thus each unit provides a portion of each of the top, bottom and longitudinal side Walls of the membrane.

-In order that the invention may be clearly understood, one specific constructional example thereof will now be described with reference to the accompanying drawings, wherein:

FIG. 1 is a perspective transverse sectional view of a marine tanker showing a membrane tank mounted in a hold of the tanker with the near end wall of the tank, which usually extends transversely of the length of the tanker, removed;

FIG. 2 shows in perspective adjacent portions of the top and end wall of themembrane of the tank shown in FIG. 1, forming part of the corner thereof, and of a sheet forming a key or anchoring member of quadrant cross-section secured to the end wall;

FIG. 3 is basically identical with FIG. 2 but additionally shows the adjacent portion of a longitudinal side wall of the tank, and two sheets forming adjacent keys together of quadrant cross-section and secured respectively to the top and end walls anking the common corner and intended to be received in a common keyway, and a further sheet forming a key of quadrant crosssection secured to the end wall at the junction with the side wall constituting a further corner of the membrane;

FIG. 4 is a vertical longitudinal cross sectional view through the junction of top and end walls of the cargo hold and membrane tank therein showing part of the thermal insulation and of the primary barrier or membrane and the secondary barrier of the tank; and

FIG. 5 is a vertical transverse cross sectional view through the junction of top and side walls of the cargo hold and membrane tank therein shown in FIG. 4.

Like parts are indicated by the same references throughout these figures.

FIG. 'l shows a marine tanker for the transport of liquefied natural gas and including thermally insulated cargo tanks supported in cargo holds and having the general configuration of said holds. In this case, the ship is provided with an outer hull 1 and an inner hull 2, which serves as the rigid shell of the membrane tank. Therefore, in the following, the inner hull 2 will be called the rigid shell 2, Ship or deck plates are indicated at 3 and the transverse bulkhead defining one end of the cargo hold is shown at 4 (FIG. 4). The rigid shell 2 is internally lined with heat insulating material indicated generally at 5 (FIG. 1). Disposed -within the shell 2 is a membrane tank, indicated generally at 6, having a primary barrier or membrane indicated generally at 7 of thin sheet Invar which, as shown in FIGS. 4 and 5, is anchored to supporting load-bearing thermal insulation by means indicated generally at 8, which is in turn, as described in the specification of U.S. Patent No. 3,112,043, carried by a substantial layer of balsa wood indicated generally at 9 and timber ground strips 11 which together serve to transmit loads to the shell 2, or the plates 3 or bulkheads 4, as the case Imay be.

The layer or balsa wood constitutes a secondary barrier and is formed by panels 10 having a balsa Wood core 12 and plywood faces 13 and 14, bonded to the core 12 by a suitable adhesive.

The timber ground or fixing strips 11 are attached at regular intervals to the rigid shell 2, plates 3 and bulkheads 4. The spaces between the strips are preferably filled with glass fibre. The outer edge of each panel 10 contacts and is bonded to the inner surface of a fixing strip 11 so that adjacent panels are inter-connected in such a way that a Huid-tight joint is formed. The panels are held in place by means of threaded Nelson studs 15 welded to the shell 2, plates 3 and bulkheads 4. 'Ihe cores of the panels 10 are provided with large holes 10a and the outer faces 13 are provided with relatively small holes 13a in alignment with each hole 10a. The stud 15 extends through the hole 13a and into hole 10a. The threaded end of the stud 15 is provided with a washer 1-6 and a nut 17. The holes 10a are preferably filled with a suitable foamed plastic, for example compressed polyvinyl chloride foam 18. Three-ply glass fibre cloth patches 19 are laminated with cold setting resin over and to seal the hole 10a.

The secondary barrier is designed to remain fluid-tight notwithstanding contractions of the panels 10. Thus, as described in U.S-. Patent No. 3,112,043, the edges of adjacent panels 10 are bevelled so that there is a gap between adjacent panels, widening in the direction of the inner surface of the panels, which is filled with foamed plastic material 20 compressed to at least 90% of its free volume. The gaps between adjacent panels 10 are closed by a scab 21 of plywood overlapping and bonded to the panels of each side of the joint. The gap between the panels 10 at the corner is lled with foam plastic material 22 identical with material 20. A corner scab 23, preferably of a strong plywood, closes the gap between the adjacent panels 10.

The tank 7 of the present example has the prismatic shape shown in FIG. 1 and is fabricated from sheets of Invar. In accordance with one aspect of the invention a series of transverse expansion joints 24 (FIG. 4) are provided in the top 7a, bottom 7b, and side wall 7c of the tank, which extend longitudinally of the ship and are subject to both thermal and ship stresses, while the end walls 7d (FIG. 5) of the tank, which are subject primarily to thermal stresses only, are fabricated without expansion joints.

In constructing such a membrane tank, large sheets of Invar are assembled and welded together in the cargo hold, or alternatively, are pre-assembled into units in the welding shops. Such a membrane may be constructed from a plurality of constructional units each of which is of annular or frame form and has secured thereto narrow strips of the same alloy constituting flanges 7e. The adjacent constructional units are connected together by Welding of the free edges of adjacent flanges which constitute expansion joints, as shown at 71 in FIG. 2. Thus each unit provides a portion of each of the top 7a, bottom 7b and longitudinal side walls 7c of the membrane.

In accordance with the present invention the corners of the membrane 7 of the tank are anchored so as to hold the membrane against overall dimensional change. The load upon the anchorages holding the membrane is considerable. Thus there are stresses acting in the plane 0f each wall due to the tendency of the wall to contract, i.e. thermal stresses, and also other streses, i.e. ship stresses. In the illustrated membrane stresses in the planes of the top, bottom and side walls along the longitudinal axis, i.e. the fore/aft axis, of the ship, are accommodated by the joints 24 (FIG. 4), so that the loads exerted upon the anchorages of the transverse corners, eg., those designated K and L in FIG. 1, of the membrane, i.e. those at the opposite ends of the tank, are not high. However, thermal stresses exert forces in the planes of the walls along axes at right angles to the longitudinal axis upon the means anchoring the longitudinal corners of the membrane, i.e., those adjoining adjacent ones of most said walls, e.g., those designated A, B, D, C, E, F, G, H, I and J in FIG. l, so that there is a considerable load on the anchorages of said longitudinal comers.

The end walls 7d of the tank supported by the transverse bulkheads are not subjected to high ship stresses and, because the walls are of a material of a low co-efcient of thermal expansion, are not subjected to high thermal stresses in the planes of the walls and do not produce high loads upon the corners.

In accordance with the present invention the walls are provided with anchoring members or keys, indicated generally at 25, extending along the corners of the membrane and constituted by sheet metal folded to form tubular members of segmental cross section.

In constructing the end walls 7d where they meet the top wall 7a, a sheet of Invar indicated generally at 26 (FIG. 2) is folded to form a part of the end wall and a part of the top wall. The end portion of part 26 in this case has a slightly offset end portion 26a adapted to receive an adjoining sheet 76, to which it can be lap welded. Such an offset end portion is not essential. The top portion of part 26 on the other hand has a downturned end portion constituting one of said flanges 7a adapted to form, with a flange 7a of an adjacent sheet, part of an expansion joint 24 (FIG. 4) when welded together in known manner.

There is attached to the part 26 at the corner thereof, forming a transverse corner of the membrane, thin sheet Invar 27 which is adapted to form outside of and at the corner a hollow tubular member of quadrant cross section 27 filled with a suitable load-bearing material 28, such for instance as a cured epoxy resin, capable of withstanding heavy loads, and constitutes a key or anchoring member extending along the corner and anchoring the end wall against the stresses acting in the planes of the walls. Any stresses in the top 7a acting along the longitudinal axis of the tank are accommodated by the expansion joints 24. The curved outer surface of the quadrant 27 conforms with and fits snugly within the internal surface of the corner scab 23 constituting the external corner of the insulation 9.

Reference to FIG. 3 serves to illustrate the treatment involved when an end 7d, top 7a and side wall 7c meet. In this case a portion of the end wall 7d is a sheet of Invar 26 to which is attached a hollow quadrant 27 as already described. The sheet 26 abuts a sheet 29 forming part of the side wall 7c and Welded to the edge thereof and is also welded to a further thin sheet of Invar 30 adapted to form a further hollow quadrant 25 opposite the corner and shown in dotted lines and filled with filling material. The sheet of Invar 29 is folded to form an inturned flange 7e. These flanges in the top and side wall portions together form a corner flange adapted for fusion welding with corresponding flanges in adjacent sheets, thereby forming part of expansion joints 24 extending transversely of the membrane. Where the edges of these two parts of the top and side walls adjoin one another there is welded to each part a thin sheet of Invar 32, 33 to form outside of and opposite the corner a pair of hollow tubular profiled members of segmental cross section constituting anchoring members or keys. Member 32 holds the top against stresses acting in its own plane and member 33 holds the side wall 7c against stresses acting in its own plane.

Because the expansion joints 24 in the top, bottom and side walls extend in only one direction, loads due to thermal and ship stresses in these walls acting in the planes of the walls transverse to the longitudinal axis of the ship must be held by the members 32, 33.

In order that these two anchoring members 32, 33 can be accommodated in a common keyway on the insulation 9 they are disposed immediately adjacent to one another. In fact, the two members are welded together to form a member of quadrant section which is, in effect, partitioned or bisected as shown in FIG. 3. The two members are filled with a load-bearing material 28 such as a cured epoxy resin capable of withstanding heavy loads.

FIG. 4 shows the anchoring member 27 located and anchored within a corner of the thermal insulation 9. Thus, there is rigidly attached to the insulation 9 loadbearing insulation blocks or stops 34 and 35 secured respectively to the top insulation and end wall insulation. A keyway 38 is formed to receive the anchoring member 27 by the insertion of hard wood wedges or filling pieces 36 and 37, the keyway being formed therebetween. Thus the lling pieces flank the anchoring member. With such an arrangement the loads due to stresses acting in the planes of the adjacent end and top Walls forming the corner are effectively restrained by the anchoring members and stops 34 and 35 thus preventing any distortion or collapse of the corner. Angle irons 39, 40 are secured respectively to the deck plates 3 and shell 2 and abut against the edges of the relevant ones of the strips 11 at the sides of the latter remote from the corner and constitute final stops to which the loads on the anchoring member 27 and stops 34, 35 are transmitted.

A similar arrangement is adapted for the anchoring members 32, 33 and serves to oppose the stresses prevailing in the top and side walls of the membrane transversely of its length as shown in FIG. 5. The two anchoring members 32 and 33 are together attached to the longitudinal corner of the membrane located and anchored within a corner of the thermal insulation 9. Thus, there is rigidly attached to the insulation 9 load-bearing insulation blocks or stops 34' and 35 secured respectively to the top insulation and side wall insulation. A keyway 38 is formed to receive together the anchoring members 32, 33 by the insertion of hard wood wedges or filling pieces 36' and 37, the keyway being formed therebetween. With such an arrangement the loads due to stresses acting in the planes of the adjacent end and top walls forming the corner are effectively restrained by the anchoring members and stops 34, 35 thus preventing any distortion or collapse of the corner.

Angle irons 39', 40 are secured respectively to the deck plates 3 and bulkhead 4 and abut against the edges of the relevant ones of the strips 11 at the sides of the latter remote from the corner acting in the same manner as angle irons 39, 40.

The spaces intermediate the blocks 3S and 3S' between the membrane walls and the insulation 9 are filled with flat faced balsa wood.

It will be understood that many, if not most, of the individual sheets forming a wall or walls of the membrane tank may require to be anchored to the supporting load-bearing insulation and such anchorages, not shown in the drawings, but similar to those shown, would for instance apply to those sheets which are not located at and do not form part of a corner of the tank.

It will be further understood that at corners where the walls do not lie at right angles, e.g. the corners designed C, D, E and F in FIG. 1, the provision of external anchoring members will be designed to resist the opposing loads due to stresses in the adjoining walls flanking the corner.

It will be apparent that the embodiments shown are only exemplary and that various modications can be made in construction and arrangement within the scope of the invention.

I claim:

1. A container for cryogenic liquids,

(a) said container having at least two externally supported walls closely approaching each other at an angle defining a wall corner, the adjacent edges of said two walls at said corner being slightlyl spaced to define an elongated slot between said two walls at said corner,

(b) each of said walls being of structurally rigid insulating material capable of bearing a substantial load,

(c) a thin liquid-tight sheet metal membrane covering and supported by the walls of the container to define the interior surface of the container, said membrane having at least two sheets corresponding to and respectively lying against said two walls, said two sheets meeting at an angle defining a continuous sheet corner corresponding to said wall corner,

(d) an elongated anchoring key attached to said membrane at said sheet corner independently of said Wall structure and comprising a piece of thin sheet metal folded to form a tubular key portion which portion is filled with load-bearing material, said key lying on the other side of said slot from said membrane, said key being supported by the adjacent edges of said wall at said corner.

2. A container for cryogenic liquids,

(a) said container having at least two walls closely approaching each other at an angle defining a wall corner, the adjacent edges of said two walls at said corner being at right angles to each other and slightly spaced apart to define an elongated slot between said two walls at said corner,

(b) each of said walls being of structurally rigid insulating material capable of bearing a substantial load,

(c) a thin liquid-tight membrane covering and supported by the walls of the container to define the interior surface of the container,

(d) an elongated anchoring key attached to said membrane at said corner independently of said wall structure, and supported by the adjacent edges of said wall at said corner,

(e) said key being attached to said membrane at said corner by means extending through said slot,

(f) said key being constituted by a piece of thin sheet metal which is folded to form a tubular key portion filled with load-bearing material,

(g) said tubular key portion being of quadrant cross section, with the straight sides of the quadrant abutting the respective edges of said wall at said corner.

3. A container according to claim 2, said key being formed of two adjacent key units, each key unit having a profile such that the two adjacent key units together form a combined key of quadrant cross section.

4. A container for cryogenic liquids,

(a) said container having at least two walls closely approaching each other at an angle defining a wall corner,

(b) each of said walls being of structurally rigid insulating material capable of bearing a substantial load,

(c) a thin liquid-tight membrane covering and supported by the walls of the container to dene the interior surface of the container, said membrane having at least two sheets corresponding to and respectively adjacent said two walls, said two sheets meeting at an angle defining a sheet corner corresponding to said wall corner,

(d) an elongated anchoring key attached to said membrane at said sheet corner independently of said wall structure,

(e) a keyway defined by two blocks of rigid insulating material respectively secured to the two interior faces of said walls, and two filling pieces respectively inserted between the two blocks and the corner and slightly spaced apart so that adjacent inner faces thereof define the keyway and retain the key member in position.

5. A container according to claim 4 wherein the membrane is of metal, and is provided with expansion joints in some of the walls only, the remaining walls not being provided with such expansion joints.

6. A container according to claim 5, wherein the cxpansion joints are parallel to each other and extend in one direction only.

7. A container according to claim 5, which is adapted to be mounted in the cargo hold of a marine tanker, those walls of the tank extending along the longitudinal axis of the tanker being provided with said expansion joints in one wall communicating with the joints or formations in an adjacent wall, the walls extending transversely of said axis not being provided with expansion joints, but being of a material in which the ratio of elastic stress to thermal stress is equal to or greater than one.

8. A container according to claim 7, wherein each of said walls is faced, at least on the inner side, with plywood sheets.

References Cited UNITED STATES PATENTS 264,764 9/ 1882 Robinson 217-3 2,373,221 4/ 1945 Blaylock et al 220-63 2,485,647 10/ 1949 Norquist 217-3 X 2,145,613 1/1939 Shenk et al 220-63 2,833,631 5/1958 Rossheim et al 220--63 X 3,030,669 4/1962 Dosker 114-74 X 3,085,708 4/ 1963 Dosker 220-9 3,088,621 5/1963 Brown 220--9 3,337,079 8/1967 Clarke et al. 114-74 X FOREIGN PATENTS 550,785 5/1930 Germany.

JOSEPH R. LECLAIR, Primary Examiner JAMES R. GARRETT, Assistant Examiner U.S. Cl. X.R. 

